1. Field of the Invention
The present invention relates in general to a method of producing a grinding wheel by using diamond particles as an abrasive material, and a cast iron as a bonding agent for holding the diamond particles together in the form of a desired shape. More particularly, the invention is concerned with an effective method of manufacturing a cast-iron bonded diamond wheel, which requires a simple sintering step that does not cause deterioration of the diamond particles due to oxidation.
2. Discussusion of the Prior Art
For bonding diamond particles for a diamond grinding wheel, there are known several types of bond, for example, metal bonds, resinoid bonds, vitrified bonds, and electrodeposited bonds, which are selected depending upon the required properties of the diamond wheels for specific grinding operations. In particular, metal bonds are generaly suited to diamond wheels for grinding hard and brittle material such as ceramics, stones, glass and concrete. Among these metal bonds for the diamond wheels is available a cast iron bond.
A cast-iron bonded diamond wheel is manufactured by preparing a powder mixture of suitable diamond particles and cast iron particles, molding the prepared powder mixture into a desired shape, and sintering or firing the obtained formed body. The sintering of the formed mass of the cast iron bond and the diamond abrasive must be effected for complete sintering of the cast iron particles, without deterioration of the diamond particles. However, the optimum range of sintering temperature of the cast iron bond is comparatively narrow, i.e., between 1125.degree. C. and 1150.degree. C., while the diamond is oxidized in air into carbon dioxide, with its weight being reduced, at 600.degree. C. or higher. Therefore, the sintering temperature and atmosphere are key factors that affect the quality of the cast-iron bonded diamond wheels.
To avoid such deterioration of the diamond particles due to oxidation, the heating to sinter the formed mass of the cast iron and diamond particles has been conventionally practiced within a heating furnace which contains a non-oxidizing atmosphere such as hydrogen or cracked ammonia gas. In the case where either of these furnaces is new or used after a long period of non-use, the diamond particles are subject to deterioration due to the presence of a certain amount of adsorbed gases on the wall surfaces of the furnace, which results in undesirable quality of the sintered diamond wheel. In other words, the sintering process using such heating furnaces requires a long pre-production or monitoring run, before the quality of the sintered products reaches a satisfactory level.
Further, the sintering operation using a heating furnace containing hydrogn or cracked ammonia gas requires a complicated procedure for loading the furnace with unsintered formed bodies of cast iron and diamond, by use of a sintering boat. Described more specifically, a layer of alumina powder is first formed over the surface of the sintering boat, and then the unsintered formed bodies are placed on the alumina layer. Finally, the formed bodies on the boat are covered with a thin layer of cast iron powder. These complicated procedure is necessary in order to minimize undesirable effects of oxygen and other gases within the heating furnace, when the formed bodies of cast iron and diamond are sintered therein.